There is a considerable body of literature describing the potential for evolving proteins for a variety of characteristics, especially enzymes for example, to be stabilized for operation at different conditions. For example, enzymes have been evolved to be stabilized at higher temperatures, with varying activity. In situations where there is an activity improvement at the high temperature, a substantial portion of the improvement can be attributed to the higher kinetic activity commonly described by the Q10 rule where it is estimated that in the case of an enzyme the turnover doubles for every increase of 10 degrees Celsius. In addition, there exist examples of natural mutations that destabilize proteins at their normal operating conditions, such as wild-type temperature activity of the molecule. For temperature mutants, these mutants can be active at the lower temperature, but typically are active at a reduced level compared to the wild type molecules (also typically described by a reduction in activity guided by the Q10 or similar rules).
It is desirable to generate useful molecules that are conditionally activated, for example virtually inactive at wild-type conditions but are active at other than wild-type conditions at a level that is equal or better than at wild-type conditions, or that are activated or inactivated in certain microenvironments, or that are activated or inactivated over time. Besides temperature, other conditions for which the proteins can be evolved or optimized include pH, osmotic pressure, osmolality, oxidative stress and electrolyte concentration. Other desirable properties that can be optimized during evolution include chemical resistance, and proteolytic resistance.
Many strategies for evolving or engineering molecules have been published. However, engineering or evolving a protein to be inactive or virtually inactive (less than 10% activity and especially 1% activity) at its wild type operating condition, while maintaining activity equivalent or better than its wild type condition at new conditions, requires that the destabilizing mutation(s) co-exist with activity increasing mutations that do not counter the destabilizing effect. It is expected that destabilization would reduce the protein's activity greater than the effects predicted by standard rules such as Q10, therefore the ability to evolve proteins that work efficiently at lower temperature, for example, while being inactivated under their normal operating condition, creates an unexpected new class of proteins we refer to as conditionally active biologic proteins.
Throughout this application, various publications are referenced by author and date. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the disclosure described and claimed herein.